It is known, for example, to supply chemicals as concentrates in powder form where the concentrate is mixed with water in order to produce a chemical of the required strength. The chemical concentrate may be hazardous to handle. The concentrate will normally be packaged in some form of container and the careful opening of the container may prove awkward or difficult. Furthermore emptying the chemical powder from the container can produce a significant amount of dust which may create a hazardous working environment. From an environmental point of view it is usually desirable, and in some cases essential, that the containers in which the chemicals are supplied be washed or otherwise treated in order to remove most, if not all, traces of the chemical from the container before it is disposed of or recycled.